Concerning the notion that there may be important regional differences in genetic load: guys, at this point they’re not hypothetical. Last year they were, and I kept my suspicions to myself, but now they’ve been seen, been measured. It is still early days, so I wouldn’t yet bet my life on their reality, but the odds are high that this pattern is real. Explaining why these differences should not exist is not going to get you very far.

Having more genetic load can’t be good. This we can be sure of. On the other hand, we don’t know just how important it is. Theory says that it is likely very important, particularly in the most complex adaptive systems. Brain function is surely the most complex of all. Once we know how IQ varies with genetic load within some population, we will have a better handle on its importance. As yet we do not really have that info – just a couple of very preliminary measurements – one that suggests that more deletions are bad for your IQ, another that suggests that people who have very high IQs (or are very tall) have less rare variation than average. Note: most rare variation is likely to be bad for you, according to theory. The measurements we would like to see will come from high-accuracy whole-genome (or at least whole-exome) data, but we may not see that info for several months…

None of this implies that there are no other factors influencing the distribution of IQ, or its evolution. Strong selective pressures could keep IQ high in environment A, even if environment A had a somewhat higher mutation rate than environment B. But all else equal – including selection pressures – IQ ought to be lower in a population that has lived for a long time in the environment with the higher mutation rate. By a ‘long time’, I think we’re talking something like a few thousand years, judging from the fact that most mutations that do anything negative at all have a small effect, say 1%. Their effects predominanate, given time, but the characteristic time should be on the order of 100 generations. You might want to look up the meaning of the phrase ‘on the order of’ – this is a rough estimate.

Strong-enough selective pressures could keep any function working well in a high mutation environment (assuming strong truncation selection) , but this is easier for simpler functions. For example, the fraction of kids who are born deaf for genetic reasons is something like 1 in 1500 (maybe a bit lower): while the fraction of kids born with something genetically wrong with their brain, wrong enough to noticeably screw up fitness, must be at least 1%. Probably more than that, if you add up genetic retardation, genetic schizophrenia, etc.

Such differences are compatible with the population with the higher mutational load being better at some things than the population with lower mutation load. Look, people in the tropics are better at withstanding falciparum malaria than Eskimos with zero mutational load would be: Eskimos don’t have any of the genetic malaria defenses. They don’t have those adaptations. If I look at known factors that partially explain high athletic performance in people of African descent – narrower hips, more fast-twitch muscles, a higher frequency of the wild-type version of alpha-actinin-three. more active versions of the androgen receptor, possibly different versions of myostatin – they look like adaptations, rather than differences in the noise level.

Anyhow, they’d better be compatible since A. we’ve found higher mutational load in people of African descent and B. they win the track events.

In fact, if this pattern is real and has existed for a long time, it will change selective pressures. In a high-mutation environment, brain function probably doesn’t deliver as much fitness per cubic centimeter – but those brains cost just as much per cubic centimeter. In that situation, selection would likely favor smaller brains (than it would in a lower-mutation environment). So we would expect to see smaller brains in populations with lower average IQ – not enough to explain all of the lower IQ, but some smaller – and we do. Cranial capacity varies, and much of that variation is explained by the correlation with latitude. Of course there are other possible explanations for this correlation than temperature, and they may be the real explanation, or part of it.

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62 Responses to Changes in Attitudes

It seems they could easily design a test to see what amounts of the IQ gaps between groups are attributable to mutational load. Tests 1,000 people’s IQs, then test their mutational loads, and see if the gaps differ from their standard size when you correct for mutational load. How difficult/expensive is it to measure someone’s mutational load, anyway?

No, I’m saying the study would be able to see if those differences in IQ between races are due to mutational load. Test 100 white people for IQ and mutational load, test 100 black people for IQ and mutational load, get the average IQ gap between the two groups (let’s say 10 points), then compare white people with X mutational load to black people with X mutational load, and see what the gap between the two subsets is. If, for example, the average gap is 10 points, but shrinks to five points when you compare whites and blacks with similar mutational loads, that suggests half the B-W IQ gap is due to mutational load. Doesn’t seem difficult. I don’t see what siblings would add, unless I’m misunderstanding something.

I can add a few data point to this, I have high IQ and am 5″ taller than my father, and walked at 8 months old.

My kids have inherited high IQ’s and are also tall, and the first 2 walked at 8 months old, the 3rd at 9 months old.

My 3rd kid was born when I was almost 49 yo, and the maternity hospital (NYU) asked me to participate in a 5 year study of micro-insertions and micro-deletions, associated with older parents. They tested for 180 of these and 90 other conditions, like Down Syndrome etc., on a specialized chip they had prepared. They told me to expect 3 to 5 insertions/deletions, and said that that was the normal range for someone my age. My kid’s results came back negative for everything, no known insertions/deletions?!

BTW, I am very heat intolerant, and can’t suntan, so avoid the sun/beaches at all times.

As anyone who has watched a children starting to walk knows, it’s usually all about falling. My mother describes my early steps as walking like a drunken sailor, and that’s how my kids were too. Lots of wobbling, not much falling – the greater reflex speed, prevents this.

BTW, in terms of reflexes, I started riding ponies as a 7 yo, and later horses – British saddle – and unlike most people, never once fell off. I’ve had near misses, but a combination of knee strength and being able to grab the horse’s mane reflexively, allowed me to stay on.

In terms of general physical fitness, at 2 yo my son was able to push a 4-seater couch across the living room – his grandfather is hoping he’ll be a linebacker. At 40 yo, I could bench-press 320 Lbs.

In the comments to the last thread, Jason Malloy commentedDr. Cochran notes that – complex adaptive systems, involving the functioning of many genes, should be the most vulnerable to genetic load

If so, is an implication that a combination of higher mutational rate and a selective disadvantage for evolved traits which rely on a large number of locii makes “big bang” mutations on a small number of genes relatively more advantageous…? I.e. useful mutations of large effect would still be unlikely, but more likely with the increased mutation rate, while building up by incremental advantages on lots of genes would be more difficult.

So a higher mutational rate will select towards a simpler trait architecture? Maybe QTL mapping (for any trait) would be more productive in high mutation rate populations than low mutation rate populations?

What about the most simple-minded theory of the relationship of brain size to temperature? Brains are hard to keep cool, so you economize on brain size in warm climates. Consistent with this, geographic variation in brain size is almost entirely due to variation in breadth, not length or height. You expect this on thermoregulatory grounds, just as you find that tropical populations have consistently smaller body circumferences/diameters, but not consistently smaller stature. Both brains and testicles seem to work properly only in a narrow temperature range, necessitating some awkward compromises.

Of course there’s no reason you can’t have a multifactorial explanation. This is more than likely, given that a vast range of human physical and behavioral variables correlate with latitude.

Heat dissipation is a major problem in personal computer design. A decade ago, Intel’s strategy was to just keep upping the clock speed of the CPU, but then started melting no matter how many fans they blew over them. Does this have any implications for brains?

Yes, it’s well established that there is much more genetic variability in sub-Saharan Africans than in other human populations and that this excess variability is of little or no selective value, i.e., “junk variability.” But this is most likely a result of sub-Saharan Africans staying put in the same place. Non-African humans have much less genetic variability because they descend from small founder groups who took only a subset of that variability with them on their way out of Africa.

If IQ differences are not due to gene-culture co-evolution and are instead due to differing mutation rates caused by differing mean temperatures, we should therefore see an inverse relationship between mean temperature and mean IQ among people sharing a similar cultural background. China, for instance, comes to mind. Yet mean IQ in that country seems to show no relationship with mean temperature (if we use latitude as a proxy).

Finally, we don’t see this inverse relationship in nonhuman species. Large-brained mammals are just as present in tropical regions as in non-tropical ones. Indeed, all of the great apes are concentrated in the tropics, while smaller-brained monkeys are found at much higher latitudes.

Yes, I read the post. “Loss of function” mutations are alternately described as deleterious or neutral. It’s a difficult judgment call at best. In a sense, no mutation is completely neutral.

And again, the example of China is instructive. If we control for culture, there should still be a north-south gradient, according to the genetic load hypothesis. Yet no such gradient is visible. Nor do we see a north-south gradient among Amerindians, who have inhabited the western hemisphere for 12,000 to 15,000 years. That’s at least 500 generations.

Actually I did find a shallow North-South cline in the Americas back in 2006. While I have not yet assembled all the numbers from my own collection of studies, just looking through some of the South American studies suggest the differences are even more pronounced:

“When we take the weighted average of all the American groups, using the numbers in Lynn’s book, we get an IQ of 90 for the Arctic people, 88 for North American Indians, and 86 for South American Indians. Since the sub-Arctic Indians living below the Eskimos scored almost as highly, perhaps there is a cline in intelligence down the continent, that may have reversed approaching the frigid area of Tierra Del Fuego, where brain sizes again inflated. “

Also, be sure to see blogger “Chuck’s” comment on the Unz piece.
“Unz’s claim: “Thus, almost two-thirds of the IQ gap between American-born Mexican-Americans and whites disappeared in two decades, with these results being based on nationally representative American samples of statistically significant size.”

Unz bases his claim of a gap narrowing on two data sources, the General Social Survey and the NLSY 97. I was unable to replicate the cited GSS findings. Below are the results of my own analysis, with search variables noted. Based on the results, the gap in the 2000s is no less than 0.7 SD. In the first table, Mexicans were identified with the “Specified Hispanic” variable, for which there was only data since 2000; the gap was 0.77 SD. In second table, Mexicans were identified through the country of origin Variable “Ethnic.” For this variable, there was data from the 70s through 2010. The gap in 2000 was 0.67 SD. This GSS gap of around 0.7 SD is approximately the same size as that found between non Hispanic Whites and 2nd generation Mexicans in the nationally representative ADD health (1994-1995) sample, which can be analyzed online. That gap was approximately 0.72 SD…

Other data comes from Jason Richwine’s analysis of the 2003 New Immigrant Survey (Richwine 2009) – which was based on a nationally representative sample of immigrants. In this sample, 2nd generation Mexicans performed 1.2 SD below non-Hispanic Whites on the very culturally reduced backwards digit span (which was given in Spanish for those wishing so).

There are other data points to consider. Based on Roth et al.’s 2001 meta-analysis, the Hispanic –White difference, between 1970 and 2000, was .72 SD (N>5 million). Mexicans comprise 2/3rds of the US Hispanic population and the other large Hispanics groups (e.g., Puerto Ricans) score little worse than them, so this is probably a fair index of the Mexican IQ between those time intervals. With regards to Mexican IQ in particular, Linda Gottfredson reports several large studies in the Appendix section of “Implications of Cognitive Differences for Schooling Within Diverse Societies.” We have: 0.63 SD in 1974 from Jensen’s California school district study; 0.55 SD from GABT job applications from the 1940s to 1970s; and 0.65 from the 1966 Coleman report.

The various studies are summarized below. For comparison, Lynn and Meisenberg (2010) give a Mexican national IQ of 88 based on 6 IQ samples and 6 international tests. As can be seen, the Mexican in the US Flynn effect has yet to occur.”

The Eskimo have high IQ relative to both the world average, and especially compared with lower latitude hunter-gatherers (the more appropriate comparison group, IMO). Latitude is one important variable, but not the only, or even primary, variable that has operated on human intelligence.

The answer to that always struck me as obvious, if you define “always” as “since the time I read the 10k explosion”. Eskimos had a much smaller population than Han Chinese, this means natural selection road tested far fewer new genes among them than among the Han. Why is the population that much smaller?

I’m surprised one would have to ask, because of climate conditions they didn’t go through the farming revolution that arguably sped up human evolution elsewhere. And the revolution seems to have started latter in the other New World people anyway.

What’s really interesting is how eskimos defy naive expectations of “hyper-mongoloidness” in a lot of physical attributes:

The Arctic (Eskimo) type is distinguished by the following characteristics: the skin is swarthy [yea, I know the fish/vitamin D explanation], the eyes are dark and almost without mixed shadings, the hair is often of a raven-black color and is very coarse, epicanthus is weakly developed (by Mongolian standards), beard and eyebrow growth is comparatively heavy. The face has less prominent cheekbones than the Baykal type and is comparatively prognathous, long, and broad. The nasal root is comparatively high; the prominence of the nose is, on the whole, greater than in the Baykal and Central Asiatic types. The lips are thick. This type is characteristic of the peoples of northeastern Siberia, the Eskimos and Chukchis. (M.G. Levin 1963)

Some people also assume they have round heads “for heat conservation”, too. Well, it’s not as straightforward as that … some eskimo populations are brachycephalic and others (famously) are very dolichocephalic.

It implies exaggeration along in a Mongoloid direction on a Mongoloid-outgroup vector.

But then, what’s the outgroup? Different chararacteristsics will be “hyper-Mongoloid” when Caucasoids are the outgroup than when Africans are the outgroup, still different ones if an average of Caucasoids and Africans are used as the outgroup (before even considering other groups).

Thick lips would be a hyper-Mongoloid trait if an average of all Mongoloids from SE Asia and Central East Asia is compared against an average of all Caucasoids. But then, not if an average of all Mongoloids from SE Asia and Central East Asia is compared against Africans….

Saying that low mutational load is “good” or what have you is a normative statement. Saying that more intelligence, or more symmetry, or more height or what have you is monotonically “good” is an ethical rather than scientific statement.

If by “good” you simply mean good for fitness then that makes sense. But that’s not how most people would read it.

Acromegaly is a serious illness – it might be worth asking your doc whether he recommends you have a blood series for Growth Hormone. It might help him if you take along photos of yourself now and ten years ago. Have you needed larger shoe sizes recently, or glove sizes, or do you have a ring that seems tighter than it used to be? These are the sort of questions he’ll ask you.

P.S. I am not a medic, just a family member of someone afflicted with the condition. So my words are not advice, just thinking out loud.

My own instinct/ prejudice is to assume that it is differences in (evolved) mechanisms for prevention and repair of mutations that make the difference in the accumulation of mutations, rather than differences in the incidence of mutations.

Would the higher rate of mutations show up as higher cancer rates? Or higher rates of rare and nasty genetic disabilities?

Alternatively, if the effect was driven by hot testes leading to mutations in sperm cells, would we see a lot more mutations on the Y chromosome than elsewhere, and cold-weather levels of mutations in mitichondria?

The bigger question Cochran is trying his best to answer is why is their such a large variation in human intelligence. So far things aren’t adding up. We can’t find any individual genes that influence intelligence more than a fraction of one percent and we know that up to one third of our genes are expressed in brain function. So from what we know so far the standard deviation in human intellegence should be really really small but intelligence tests as well as common sense from living in the everyday world tells us it is really really large. Maybe other people don’t appreciate just how important it is to find out what makes us so variable in intelligence but I do.

Do you know what seven billion extra smart monkeys hanging out in the year 2012 are are doing? Killing time, wasting space, making plants and animals disapear to make more room for their collective fat asses. Meanwhile back at the ranch a few people are slowly making headway on The Big Question, what genetically causes such a large variation in human intelligence. Someday hopefully a lot closer in the future than the advent of the industrial revolution is in our past this question will be answered. Francis Crick, Mr I discovered DNA, threw out a long time ago that there will be analogies to be drawn between the eye and the brain. I’m guessing he is right, that as a perfectly round eyeball is nessecary for clear vision a perfect symmetry of uncounted genes is required for high intelligence. Is Cochran right that a genetic load of deleterious genes is a very important factor in causing the large variation in human intelligence? I simply don’t know. I just wish there were another 10,000 Greg Cochrans out there trying to answer what I call The Big Question. It is the big question because when we answer it then we are on the verge of fixing the game that so far has just been the rsult of random chance.

So, what organ systems should be hit hardest and least hard by higher number of slightly deleterious mutations? From this article I gather that along with brains, testes and kidneys seem to express a lot of different genes, whereas muscles and livers, muscles, and hearts express a relatively smaller number. So if this higher rate of slightly deleterious mutations is having a bad effect on blacks, it ought to show up in kidney function (maybe causing higher blood pressure due to too much salt?) and in testes function (I’m not sure how that would manifest, since anything that messes up reproductive machinery ought to get selected against really strongly).

My point is that if a gene messes up something on the critical path of reproducing, it’s going to have a higher fitness cost than a similar-sized messing up of something happening a little further away from direct reproduction. This is why it seems really hard to imagine a homosexual recessive gene, right? A mutation that makes you a little less able to fight off infection may still let you leave offspring, since maybe you will still be healthy enough otherwise or you will live in a time/place with relatively few of the kind of pathogen you’re weak against. A mutation that causes you to have heart problems in your 40s lets you leave offspring, since you’ve probably had most of the kids you were going to have by the time the heart attack kills you off. A mutation that causes a drop in sperm count or a loss of sex drive or loss of interest in women or something is a lot more directly linked to fitness–you just don’t have any/many kids, and so the mutation gets selected out pretty quickly.

Consanguineous marriage would presumably reduce the prevalence of many of the most deleterious mutations.
“The highest rates of consanguineous marriage occur in north and sub-Saharan Africa, the Middle East, and west, central, and south Asia.”
What would the effect of polygyny be on the prevalence?

Unz is a smart guy, but he so obviously has already made up his mind on the subject of Mexican immigration, that all of his arguments seem somewhat suspect until proven otherwise. I mean, I would be very surprised if one could have found an argument that would have convinced C.S. Lewis that Christianity was false, or an argument that would convince Richard Dawkins that it is true; likewise, I don’t believe that there is an argument that would convice Ron Unz that more Mexican immigration is a bad thing. Obviously, this does not refute any of his substantive arguments (Peter Frost addresses these pretty well over at his site, as noted above), but let’s just say that I tend to distrust anything on Mexican immigration coming from that particular direction.

From the data in this paper, the age-adjusted rates of cancer for black men are a little higher than for white men, and a little lower for black women than white women. That doesn’t intuitively seem consistent with a higher mutation rate among blacks, does it? I mean, some of the mutations passed down should raise cancer risk (like a mutation along the sequence of mutations that turn a growth-regulating gene into an oncogene, or muttion that makes a DNA repair gene less effective). Is there some reason a bigger genetic load wouldn’t be expected to show up in higher cancer rates?

I guess some of this could be an artifact of higher levels of diagnosis among whites (hispanics and Asians have much lower rates of cancer than whites and blacks–maybe that’s consistent). That is, if whites get colonoscopies and mamograms and PSAs and such much more often than blacks, maybe they get diagnosed more often, and since some of those diagnoses wouldn’t have been the thing that killed them, maybe that could account for whites having a higher rate than hispanics and Asians. But that’s awfully damned speculative–I’d want to see data showing this effect before I believed it. I guess age-adjusted cancer mortality statistics would give a clearer picture.

The other potential biases I can think of here go the other way–blacks have worse lifestyles in most ways than whites, I think–more drinking, smoking, promiscuity, living in more polluted areas and older buildings with asbestos and lead paint and all that. To the extent money, education, higher social class, or higher IQ let you avoid cancer, whites should be getting a much bigger bonus than blacks, and yet, those rates just aren’t that different. (Whites and blacks look much more similar to each other than to hispanics and Asians. Weirdly, American Indians have really low cancer rates–it would be interesting to know why. (Bad medical care means they’re never diagnosed? All those waves of diseases when the Europeans came filtered out the unfit?)

“The age-adjusted death rate for cancer continued to decline for both white and black populations from 2005 to 2006. Rates peaked in 1990 and from 1990 to 2006 declined 19.9% for white males, 11.7% for white females, 28.4% for black males, and 14.9% for black females.”

Copied the wrong quote. Rates are now about 20-30% higher for blacks, as you can see in the linked chart. But it’s not all mutations: black male rates used to be much higher and have fallen (maybe smoking?). We know from heritability studies that much or most variation in cancer is environmental. With a 20-30% higher mutation rate for blacks, that might mean a 10% boost in cancer rates, smaller than the effects of behavioral differences, urbanization, and other such factors.